Continuous Crawl is a new feature introduced in SharePoint 2013 Search.

The idea of the feature is to:

Keep the Results as Fresh as possible

How it works?

Continuous crawl crawls content that was added, changed, or deleted since the last crawl. Continuous Crawl starts at pre-defined time intervals. The default time interval is every 15 minutes. Multiple continuous crawl can run simultaneously.

How to configure?

To enable Continuous Crawl for a a Content Source, Please follow the steps below.

Open Central Administration > Service Applications > Search Service Application

Click on the Content Sources link as highlighted above.

In the appearing page click on the Local SharePoint Sites item. You will get the page below. Scroll down & Check the Enable Continuous Crawls option under the Crawl Schedule section.

Click the OK button to save changes. You are done with enabling Continuous Crawl.